The invention described herein relates generally to X-ray lasers, and more particularly to improved means and methods for driving X-ray lasers.
The first operational conventional-laser-driven X-ray laser is taught by Campbell et al in U.S. Pat. No. 4,827,479 issued May 2, 1989. This X-ray laser was described by Rosen et al in Physical Review Letters 54, 106 (1985), and the experimental demonstration of the X-ray laser was set forth by Matthews et al in Physical Review Letters 54, 110 (1985), with news of the X-ray laser having been reported in Physics Today, March 1985, at pages 17 to 19. Other known X-ray lasers are described by MacGowan et al in Physical Review Letters 59, 2157 (1987), and by Eder et al in J. Opt. Soc. Am. B 4, 1949 (1987).
X-ray lasers are reviewed by Matthews and Rosen in their article "Soft-X-Ray Lasers", Scientific American, December 1988, at pages 86 to 91, incorporated by reference herein. At page 88, and following, the article states, ". . . to achieve a robust population inversion in soft-X-ray lasers one not only must supply 1,000 times as much energy as for an optical laser but also must supply it roughly 10,000 times as fast. To do this, high-power optical lasers are employed as pumps. At the LLNL (Lawrence Livermore National Laboratory) the pumps are two beams of the 10-beam NOVA, the world's most powerful laser . . . , which is capable of delivering up to 10.sup.14 watts in a pulse of less than a nanosecond. . . . In the X-ray lasers now operating at the LLNL, the NOVA beam strikes a thin foil of, say, selenium, yttrium or molybdenum . . . . In fact, when the NOVA beam strikes the foils, it vaporizes them completely and creates a plasma in which, for example, selenium atoms (with 34 electrons) are stripped of their outer 24 electrons. The electrons freed by the intense NOVA beam are of high energy - 1,000 electron volts (1 keV) or, equivalently, a temperature of 10 million degrees Kelvin. . . . At the LLNL the selenium foil is actually a layer about 75 nanometers thick, several millimeters wide and several centimeters long, which is deposited on a vinyl substrate to give it rigidity. Special lenses focus the NOVA beam to a line of about the same length but 0.1 millimeter wide. When such a line-focused light pulse from NOVA strikes the selenium target, the thin selenium foil is heated throughout, explodes and forms a cylindrically shaped plasma about 0.1 millimeter in diameter and several hundred times that in length. The cylindrical shape provides a preferred axis for X-ray amplification: photons traveling radially pass out of the plasma, whereas photons traveling along the axis stimulate the emission of other X-rays. Since there are no mirrors, the amplification takes place on only a single pass". The article goes on to observe that seemingly ". . . devices requiring the million-gigawatt NOVA as a pump can never be made small and practical".
In the operation, for example, of a conventional-laser-driven nickel-like X-ray laser, that amplifies X-rays having a wavelength of about 45 Angstroms, the driving optical laser must typically provide an incident irradiance to the active area of the X-ray laser foil of about at least 6.times.10.sup.14 watts/cm.sup.2, in a pulse having a duration of about 1.0 nanosecond. Since in large optical systems the minimum width to which an optical laser pulse can be line focused is about 100 microns, the optical pulse must contain about 9,000 joules of energy to drive an X-ray laser that is only about 1.5 centimeters long. Optical laser pulses with such a huge energy content can only be delivered by enormous, building-sized laser systems, such as the Lawrence Livermore National Laboratory NOVA. Consequently, except at the rare and unique facilities where these immense laser systems exist, as a practical matter the usage of X-ray lasers is everywhere foreclosed. This is indeed unfortunate because the potential use of X-ray lasers in submicroscopic imaging, holography, and spectroscopy cannot go forward on a practical and widespread basis so long as X-ray lasers cannot be driven by optical lasers of relatively low energy and small physical size, and so long as methods do not exist for driving X-ray lasers with optical lasers of relatively low energy and small physical size.
As an example of these observations, Suckewer, in U.S. Pat. No. 4,704,718 issued Nov. 3, 1987, discloses soft X-ray lasing action within a recombining plasma column contained and shaped by a strong cylindrical magnetic field created by powerful 100 to 150K Gauss helical solenoid magnets. The magnetically confined plasma column is created by focusing a high energy, 1.5 KJ, CO.sub.2 laser pulse on a target such as carbon. Subsequently, a second powerful picosecond laser beam is focused along the central part of the plasma column, and a soft X-ray laser beam is stated to form in the recombining plasma of the magnetically confined plasma column. A 1.5 KJ, CO.sub.2 laser pulse must be produced by precisely the sort of immensely vast laser apparatus that has just been referred to, and whose required use so effectively precludes the free and common availability of X-ray lasers.